1. Field of the Invention
The present invention relates to a piezoelectric sounder which transmits a signal by using a sound.
2. Related Background Art
There has conventionally been known a communication method (e.g., Patent Literature 1 (Japanese Patent Publication No. 4295781)) which, by utilizing an existing speaker serving as a sounding component and a microphone mounted on a terminal such as a mobile phone, transmits a signal to the terminal through the medium of air.
Applications of the above-mentioned communication method which have recently been under consideration include transmitting program information data from TV speakers and sending data by a distance of only about several meters from small-sized healthcare devices.
However, typical speakers which have been considered for use in the above-mentioned communication method are mainly those of the dynamic type, which are very hard to reduce their size, weight, and power consumption.
Preferred for reducing the size of sounding components is a piezoelectric sounder such as the one disclosed in Patent Literature 2 (Japanese Patent Application Laid-Open No. 11-52958), which is easier to reduce the size, weight, and power consumption than the dynamic speakers. A small-sized piezoelectric sounder can achieve a case size with a diameter of 13 mm or less and a height of 8 mm or less, for example.
In such a piezoelectric sounder, the frequency band of 16 to 20 kHz is suitable for short-distance communications, frequencies lower than 16 kHz make sounds easier to hear and thus are unsuitable for communications, and frequencies higher than 20 kHz slow down the data transmission speed and thus are unsuitable for data communications.